In pleated air filters, the dust holding capacity in high dust applications can be reduced by up to 40% or more due to improper pleat shape. Pleats that curve or are bent can block air flow from getting all the way to the base of the pleat. This is especially problematic in pleats over 2 inches deep.
As shown in FIG. 1, it is known to form filter media 2 with corrugations 4. The corrugations 4 help give the media 2 stiffness. The corrugations 4 are typically large in frequency and small in amplitude and are often insufficient to maintain the pleat straightness during the pleating process. This may cause a bend or curve in the final pleated and folded filter formed with the filter media 2.
In some situations, filter media manufacturers address the above noted issues by increasing the basic corrugation amplitude and reducing the frequency of the corrugations (e.g., to approximately four corrugations per inch). However, increasing the corrugation amplitude and reducing the corrugation frequency can be an expensive because it requires precise control of paper conditions (i.e., if done in-house by a filter manufacturer) and/or require retooling of media manufacturing devices (i.e., if done by a paper mill). Further, the resulting media is difficult to handle, and the large corrugations will be reduced every time the media paper passes over a roller during slitting, pleating, and other manufacturing operations. In other situations, filter media manufacturers address the above noted issues by embossing a flat media by pressing the flat media with a large force. However, this requires precise control of the pleater and paper conditions to avoid tearing the paper media.